The present invention relates generally to water-soluble polyvinyl alcohol (PVOH) film. More specifically, the present invention relates to water-soluble PVOH film with particular applications for packaging of non-liquid products, such as cleansers, conditioners, disinfectants, or the like.
Polyvinyl alcohol (PVOH) is a synthetic resin generally prepared by the alcoholysis, usually termed hydrolysis or saponification, of polyvinyl acetate. Fully hydrolyzed PVOH, where virtually all the acetate groups have been converted to alcohol groups, is a strongly hydrogen-bonded, highly crystalline polymer which dissolves only in hot waterxe2x80x94greater than about 140xc2x0 F. (60xc2x0 C.). If a sufficient number of acetate groups are allowed to remain after the hydrolysis of polyvinyl acetate, the PVOH polymer then being known as partially hydrolyzed, it is more weakly hydrogen-bonded and less crystalline and is soluble in cold waterxe2x80x94less than about 50xc2x0 F. (10xc2x0 C.). Both fully and partially hydrolyzed PVOH types are commonly referred to as PVOH homopolymers although the partially hydrolyzed type is technically a vinyl alcohol-vinyl acetate copolymer.
The term PVOH copolymer is generally used to describe polymers that are derived by the hydrolysis of a copolymer of a vinyl ester, typically vinyl acetate, and another monomer. PVOH copolymers can be tailored to desired film characteristics by varying the kind and quantity of copolymerized monomers. Examples of copolymerizations are those of vinyl acetate with a carboxylic acid or with an ester of a carboxylic acid. Again, if the hydrolysis of acetate groups in these copolymers is only partial, then the resulting polymer could be described as a PVOH terpolymerxe2x80x94having vinyl acetate, vinyl alcohol, and carboxylic acid groupsxe2x80x94although it is commonly referred to as a copolymer.
It is known in the art that many PVOH copolymers, because of their structure, can be much more rapidly soluble in cold water than the partially hydrolyzed type of PVOH homopolymers. Such copolymers have therefore found considerable utility in the fabrication of packaging films for the unit dose presentation of various liquid and powdered products including agrochemicals, household and industrial cleaning chemicals, laundry detergents, water treatment chemicals and the like.
The manufacture of packaging films for liquid products poses a unique concern, as they must be free of bubbles and pin holes, and capable of resisting problems such as physical incompatibility exemplified by xe2x80x9cweepingxe2x80x9dxe2x80x94a condition whereby the package contents seep from the film over a prolonged storage periodxe2x80x94caused by certain components typically used in liquid detergent products. The increased level of quality required to manufacture a film and package such liquids adds significantly to the packaged product cost.
Conversely, powdered products are far more forgiving when it comes to packaging. Pin holes and micro bubbles in the film do not present problems for packaging powdered products. Physical compatibility is less problematic, due in part to the non-existence of migrating materials in powdered detergents. Finally, weeping and early film decomposition do not commonly occur with the packaging of powdered products. For these reasons the type and quality of PVOH film used to package powered products can be significantly varied from that for the liquid counterparts.
However, those in the powdered product industry have been directed toward the use of either the higher quality, more expensive PVOH copolymer films designed for liquid product packaging or inferior films such as less diverse and more slowly soluble homopolymer-based films including films produced by blown extrusion.
The present invention has solved this problem of film quality versus manufacturing cost as it relates to packaging of powdered product, as well as other problems faced by those in the industry. By making a less expensive PVOH copolymer film having good water-soluble qualities, those in the industry have an alternative source for packaging powdered products.
A water-soluble film suitable for packaging a non-liquid product, including the method for preparing the film composition and packaging for the non-liquid product, is disclosed. In one particular embodiment of the invention, the film composition comprises a hydrolyzed copolymer of vinyl acetate and methyl acrylate in the range of from about 30 to about 95 percent by weight, modified starch in the range of from about 8 to about 30 percent by weight, plasticizer in the range of from about 5 to about 30 percent by weight, lubricant/release agent in the range of from about 0.0 to about 1.5 percent by weight, and surfactant in the range of from about 0.01 to about 1.5 percent by weight.
In a preferred embodiment of the invention, the film composition utilizes an agent to prevent color drift, particularly browning, of a polymer solution used to cast the film. Preferably the agent comprises sodium metabisulfite in an amount in the range of from about 0.12 to about 1.0 percent by weight. Most preferably, the sodium metabisulfite is used in an amount in the range of from about 0.4 to about 0.7 percent by weight.
A preferred method for preparing a water-soluble copolymer film for packaging of a non-liquid product is also disclosed and claimed. The method comprises the steps of copolymerizing vinyl acetate and methyl acrylate to form a copolymer, hydrolyzing the vinyl acetate-methyl acrylate copolymer to form a vinyl alcohol-gamma lactone copolymer having a 4% solution viscosity in the range of from about 5 to about 50 cps at 20xc2x0 C., slurrying the hydrolyzed polymer with water, adding modified starch to the copolymer-water slurry in an amount of from about 8.0 to about 25.0 percent by weight, heating the hydrolyzed copolymer and starch slurry to form a solution, treating the solution with caustic soda to create a solution of a copolymer having from about 1 to about 12 mol percent carboxylate groups, from about 0 to about 11 mol percent gamma lactone units, and from about 88 to about 99 mol percent vinyl alcohol units, and then casting the hot copolymer solution on a suitable surface to create a film having a thickness in the range of from about 0.1 to about 5.0 mils (about 0.0025 to about 0.127 mm).
A package for containing a non-liquid product is also disclosed and claimed. A preferred package comprises at least one compartment comprised of a water-soluble film comprising from about 30 to about 95 percent by weight of a hydrolyzed copolymer of vinyl acetate and methyl acrylate, from about 8 to about 30 percent by weight of modified starch filler, from about 5 to about 30 percent by weight of plasticizer, and from about 0.01 to about 1.5 percent by weight of a surfactant.
In one embodiment the package may be used to deliver a unit dose of a non-liquid agent. The preferred unit dose comprises a package comprising a water-soluble film comprising from about 40 to about 90 percent by weight of a hydrolyzed copolymer of vinyl acetate and methyl acrylate, from about 8 to about 30 percent by weight of a modified starch filler, from about 5 to about 30 percent by weight of a plasticizer, and from about 0.01 to about 1.0 percent by weight of a surfactant, and a non-liquid agent contained within the package. The non-liquid agent may be a-cleanser, a disinfectant, a polish, a conditioner, or the like.
These and other objects of the invention are disclosed and claimed in the following detailed description of the invention, including the appended drawings.